This invention relates to a compressor of the type used for air compressor, refrigeration, air-conditioning, etc., and more particularly to an oil-free scroll compressor.
An oil-free scroll compressor, which does not use oil, such as a lubricating oil, for the flow passage of the operation gas, is a well known compressor for use in air compressor, refrigeration, and air condition. In this oil-free scroll compressor, two sealed spaces are defined by wraps and end plates on the outer wall surface of an orbiting scroll wrap and a stationary scroll wrap by combining the orbiting scroll and the stationary scroll, each of which is equipped with spiral wraps perpendicular to an end plate, while the inside of the wraps face one another. The sealed spaces move towards the center portion due to the relative motion of both scrolls. As their volumes thus decrease, a gas sucked from the outer peripheral sides of these scrolls is compressed and is discharged from a discharge port disposed at the center portion of the stationary scroll. When the operation gas is compressed in this way by the relative motion of the orbiting scroll and the stationary scroll, the scroll compressor generates heat. This also holds true for other types of compressors handling gas. Japanese Patent Laid-Open No. 217580/1995 describes a two-stage oil-free screw compressor having a small capacity of 22 kW to 37 kW, for example, wherein the first stage discharge air temperature reaches about 190 to about 240.degree. C. Therefore, in the scroll compressor which is of the same displacement type, heat generation of a similar level can be expected if the compressor ratio, etc., is the same.
When the compressor generates heat, the clearance of each portion of the compressor changes from the design value due to thermal deformation, and the compressor becomes less reliable. At the same time, performance of the compressor drops due to a leakage from clearances caused by the thermal deformation, etc. Therefore, a cooling system for effectively guiding the heat generated inside the compressor to the outside has been necessary, and an example of such a system is described in Japanese Patent Laid-Open No. 217580/1995 and Japanese Utility Model Laid-Open No. 104384/1983.
According to Japanese Laid-Open No. 217580/1995, a pre-cooler for primarily cooling a gas discharged from a low pressure stage compressor element is interposed between the low pressure stage compressor main body and an intercooler in a two-stage oilless scroll compressor, and this pre-cooler is accommodated inside an exhaust duct and is cooled by exhaust air flowing through each cooler. This technique retains the effect of dissipating heat generated by the scroll compressor from the compressor to a certain extent, but is not yet sufficient for improving the reliability by cooling the compressor as a whole. In other words, though this approach considers how to cool the cooler on the discharge side of the cooling fan, it does not take cooling of the compressor element disposed on the suction side into consideration. In this regard, if the compressor element which generates a high compression heat is cooled by air, the mass of cooling air increases and a problem develops in that the noise increases due to the increase of a flow velocity inside the exhaust duct. Additionally, the compressor element, the cooling fan, the cooler, etc., are disposed plane-wise, and require a large installing space. Therefore, a reduction of the size of the compressor can not be achieved.
According to Japanese Utility Model Laid-Open No. 104384/1983, on the other hand, a compressor driven by a vertical motor is disposed below the motor, a blower is disposed above the motor, and they are accommodated in a casing so as to cool the compressor as a whole using the blower. According to this technique, however, the air steam around each portion of the compressor changes depending on the flow passage resistance, and all the heat generating portions cannot always be cooled.